A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by any one of the patent disclosure, as it appears in the U.S. Patent and Trademark Office patent files or records, but otherwise reserves all copyright rights whatsoever.
1. Field of Invention
The field of the present invention relates in general to the field of wireless broadcast of information using one or more multiple access protocols and in particular to methods and apparatus for implementing spatial multiplexing in conjunction with the one or more multiple access protocols during the broadcast of information.
2. Description of the Related Art
In wireless broadcast systems, information generated by a source is transmitted by wireless means to a plurality of receivers within a particular service area. The transmission of such information requires a finite amount of bandwidth, and in current state of the art transmission of information from different sources, must occur in different channels.
Since there are quite a few services (e.g. television, FM radio, private and public mobile communications, etc.) competing for a finite amount of available spectrum, the amount of spectrum which can be allocated to each channel is severely limited. Innovative means for using the available spectrum more efficiently are of great value. In current state of the art systems, such as cellular telephone or broadcast television, a suitably modulated signal is transmitted from a single base station centrally located in the service area or cell and propagated to receiving stations in the service area surrounding the transmitter. The information transmission rate achievable by such broadcast transmission is constrained by the allocated bandwidth. Due to attenuation suffered by signals in wireless propagation, the same frequency channel can be re-used in a different geographical service area or cell. Allowable interference levels determine the minimum separation between base stations using the same channels. What is needed is a way to improve data transfer speed in the multiple access environments currently utilized for wireless communications within the constraints of available bandwidth.
The present invention provides methods and apparatus for implementing spatial multiplexing in conjunction with the one or more multiple access protocols during the broadcast of information in a wireless network.
In an embodiment of the invention, a subscriber unit for use in a cellular system with base stations, each including spatially separate transmitters for transmitting selected substreams of at least one of a plurality of subscriber downlink datastream(s) on an assigned channel of a multiple access protocol, is disclosed. The subscriber unit includes: spatially separate receivers, a spatial processor, and a combiner. The spatially separate receivers receive the assigned channel composite signals resulting from the spatially separate transmission of the subscriber downlink datastream(s). The spatial processor is configurable in response to a control signal transmitted by the base station to separate the composite signals into estimated substreams based on information obtained during the transmission of known data patterns from at least one of the base stations or by using blind training techniques. The spatial processor signals the base stations when a change of a spatial transmission configuration is required in order to resolve the composite signals into estimated downlink datastream(s). The combiner combines the estimated substreams into a corresponding subscriber datastream.
In one embodiment, a wireless cellular remote unit is described that is suitable for transmitting a datastream to at least one base station that is part of a cellular network. The wireless cellular remote unit includes a plurality of spatially separate antennas and a transmitter. The transmitter is arranged to transmit a plurality of substreams of the datastream on an assigned channel or slot of a multiple access protocol. Each substream is applied to an associated one of the spatially separate antennas.
In some embodiments, the transmitter is responsive to a control signal from the base station to vary the number of applied substreams. In one particular embodiment, a detector is provided to detect a mode of the datastream and to generate a corresponding mode signal. A parser that is responsive to the mode signal is used to selectively parse the datastream into a variable number of substreams.
The described spatial remote unit can operate in accordance with a wide variety of multiple access protocol including code-division multiple access, frequency-division multiple access, time-division multiple access, space-division multiple access, orthogonal frequency division multiple access (OFDMA), wavelength division multiple access (WDMA), wavelet division multiple access, orthogonal division multiple access (ODMA) and quasi-orthogonal division multiple access techniques. Any appropriate access technique can be used to assign the channel or slot.
The wireless cellular remote unit can be mobile or fixed and may be used in a wide variety of applications including as stand alone units, and as network access devices that serve as a node in the wired network to provide the wired network with access to the cellular network. By way of example, the wired networks may include local area networks, home networks, wide area networks and vehicle based networks. In some embodiments, the wireless cellular remote unit is incorporated into a bridge or router to provide a wireless bridge or router.
In another implementations, the unit may be used as a wireless interface unit for a repeater base station that is used in conjunction with a master base station in a cellular network. In still other implementations, the units can be used to extend the range of DSL or cable systems.
The transmitter may be used in conjunction with a receiver having a spatial processor arranged to separate a composite downlink signal received by the spatially separate antennas into estimated substreams. The estimated substreams are combined into a corresponding subscriber datastream.